i'm running out of resealable stopper bottles. and they're expensive. can i use PET bottles instead? i think those thin ones used to bottle mineral water are too weak and could be dangerous. what about those re-usable 1.5-liter to 5-liter soft drink bottles? they're thicker and look sturdy.

oh and second question: what will reduce the danger of exploding bottles, secondary fermentation in-vat or in-bottle?

I can't help any on the first question, I would never use plasic personally though.

For avoiding bottle bombs though you want to make sure your OG reading is consistantly the same for a few days before bottling. Then you only want to add the 3/4 cup of priming sugar when you bottle.

From what I understand bottle bombs are the result of two things, one bottling a beer that hasn't completely fermented out, and two (and I'm not entirely sure this is true) is bottling a beer that is infected (can someone straighten me out on this if it is a fallacy).

In Australia Coopers market a Brown 750 ml PET bottle ,I have been using for a couple of yesrs now for All grain brews , I have no problems with it , I like to have a compact bottle for storage which is light to use and they in no way affects the tast of the beer,
I must confess I have not stored beer in them for over six months ,I drink two bottles a night and three at the weekends .so a five gallon batch only lasts me two weeks and so I cant get enough bottles.
I am told that PET over long period is porous I really had no experience of that.
I think everyone likes a glass bottle because thats what everyone expects.
Pumpy.

Last year I was experimenting and did a 7 gallon batch, & not sure of the corn sugar amount/equivalent. I was also short on bottles & no keg space, so I decided to save back a few 16oz & 2 liter soda bottles just in case. I found that the bottles showed signs of positive pressure in a few days and other than having the "clear bottle syndrome", I had great results with using them. You can ship them easier (but competitions won't except them.) And you can toss them after one use. I now use plastic pop bottles if I know I am going to drink the beer myself and have had beer stored for 4 months with excellant results.